1. Field of the Invention
The present invention relates to a cathode-ray tube having a flat face, and more particularly, to a cathode-ray tube in which the installation structure of a tension mask is improved.
2. Description of the Related Art
In a color cathode-ray tube, electron beams emitted from electron guns pass through electron beam passing holes of a shadow mask which has a color separation function and land on a phosphorescent film, and thereby excite a phosphorescent material to form images.
The screen surface of a conventional color cathode-ray tube is designed to have a predetermined curvature considering trajectories of electron beams emitted from the electron guns and deflected by a deflection yoke, and also the shadow mask is designed to have a curvature corresponding to the curvature of the screen surface. During the operation of the color cathode-ray tube having the structure as above, the shadow mask is heated by the electron beams, i.e., thermal electrons emitted from the electron guns and experiences a doming effect in which the shadow mask domes toward the screen. The doming effect causes the electron beams to land not exactly on the phosphorescent screen. In addition, since the screen surface of a conventional color cathode-ray tube has the predetermined curvature, there are problems in which the angle of view is narrow and images are distorted at the edge portions of the screen surface.
A cathode-ray tube having a flat screen surface is developed in order to solve the above problems, and comprises a flat panel provided with a phosphorescent film and a mask fixed to the panel in a state applied with a predetermined tension.
FIG. 1 shows a support system for a tension mask of a cathode-ray tube having a flat face, and the support system is disclosed in U.S. Pat. No. 4,900,977. As shown in FIG. 1, a support frame 12 is fitted to a panel 11 provided with a sealing portion 11 a along the peripheral part of the panel 11, and a tension mask 13 is fixed to the upper edge of the support frame 12.
In the above structure, the stepped sealing portion 11a must be provided along the peripheral part of the panel 11 in order to fix the tension mask 13 to the panel 11. Further, distance deviation between the tension mask 13 and the phosphorescent film formed on the inner surface of the panel 11 may be serious depending on the fixation state of the support frame 12 to the panel 11.